Horizontal deflection circuit used in television image receiver essentially serves to deliver sawtooth shaped current to horizontal deflection yoke. Generally, flyback transformer is connected as load equivalently in parallel with the horizontal deflection yoke. In addition, it is known that, in order to correct distortion of picture image known as pin cushion distortion, there is provided, as shown in FIG. 1, at the horizontal deflection circuit, a diode modulation circuit comprising a pin cushion distortion correction output transistor 151, a diode 152, a coil 153, a diode 154, a capacitor 155 and a pulse modulation transformer 156, etc.
The fundamental operation of horizontal deflection will be described below by taking the example of horizontal deflection circuit using transistor as switching element for horizontal output as shown in FIG. 1.
In FIG. 1, when, at the latter half of horizontal scanning time period, horizontal driver pulse of positive polarity is applied to base of a horizontal output transistor 131 so that the horizontal output transistor 131 is turned ON, collector current flows while linearly increasing through a primary coil 136a of a flyback transformer 136 from power source (supply terminal). Moreover, simultaneously therewith, positive deflection current flows in a horizontal deflection yoke 134 from sigmoid (S-shaped) distortion characteristic correction capacitors (hereinafter referred to as sigmoid correction capacitor as occasion may demand) 135a, 135b serving as power source (supply). Further, when the horizontal output transistor 131 is turned OFF at horizontal flyback (retrace) time period, collector current becomes equal to zero (0). In this case, while synthetic inductance of primary coil 136a of the flyback transformer 136 and the horizontal deflection yoke 134 and a resonance capacitor 133 resonate, charge current flows into resonance capacitor 133 from the horizontal deflection yoke 134 and the flyback transformer 136, and then discharge current for discharging it flows into the horizontal deflection yoke 134 and the flyback transformer 116. However, since a damper diode 132 is connected to the horizontal deflection yoke 134 and the flyback transformer 136, this resonant phenomenon stops at this stage. As a result, backward current from the horizontal deflection yoke 134 and the flyback transformer 136 does not flow in (through) the resonance capacitor 133, but flows in the damper diode 132. At this time, retrace pulse is generated in a secondary coil 136b of the flyback transformer 136. By rectifying this retrace pulse by rectifier circuit (not shown), high voltage can be obtained.
In addition, the pin cushion distortion correction output transistor 151 is caused to be turned ON at a predetermined timing corresponding to quantity of correction in synchronism with horizontal scanning to modulate current flowing in the horizontal deflection yoke 134 by waveform of a predetermined vertical period, thus making it possible to correct pin cushion distortion.
The above-described deflection operation is numerically indicated below. In this case, when maximum amplitude ((peak to peak) value which will be referred to as PP value hereinafter) of horizontal deflection current I flowing in the horizontal deflection yoke 134 is Ipp, maximum voltage of voltages V across both ends of the horizontal deflection yoke 134 is Vp, inductance of the horizontal deflection yoke 134 is L and horizontal flyback (hereinafter referred to as retrace) time period is Tre, voltage V is expressed as below. EQU V=L(dI/dt) (1)
In the case where the retrace pulse can be approximated by sine wave curve, the maximum voltage Vp is expressed as below. EQU Vp=(.pi./2)LIpp/Tre (2)
On the other hand, when CRT and horizontal deflection yoke 134 which are used are determined, energy of deflection magnetic field necessary for scanning electron beams by that horizontal deflection yoke 134 is univocally determined by shape of CRT and/or high voltage condition, etc. Since magnetic energy that current I flowing in indactance L has is expressed as (1/2)LI.sup.2, LIpp.sup.2 represents deflection efficiency of this horizontal deflection yoke 134. When this deflection efficiency is W, the following formula holds. EQU LIpp.sup.2 =W (3)
From the formulas (2), (3), the following relational expression is given. EQU IppVp=(.pi./2)W/Tre (4)
When W and Tre are constant in the above-mentioned formula (4), horizontal deflection current Ipp is inversely proportional to retrace pulse voltage Vp across the both ends of the horizontal deflection yoke 134.
Since Vp of the retrace time period is necessarily smaller than voltage across the both ends of the switching element in the horizontal deflection circuit conventionally used as shown in FIG. 1, Vp is restricted by the withstand voltage performance of the switching element. Accordingly, in the case where horizontal deflection frequency is twice grater than that of ordinary case, such as, for example, flicker free television image receiver, since Tre is caused to be 1/2. Therefore, if Vp is unchanged when viewed from withstand voltage performance of the switching element, Ipp becomes double. As a result, there increases power loss in respective elements of the circuit by the above-mentioned fact. By this countermeasure, there inevitably results increase in the cost of circuit including respective elements.